Current research in genomics, proteomics and personalized medicine requires fast, precise and high-throughput target profiling. To meet this challenge, barcode technology for massively parallel and high-throughput bio-detection has attracted much attention. Furthermore, multifunctional carriers are badly needed in the areas of disease diagnostics and therapy.
Fluorescently-labeled molecules have been used for a wide range of applications. Typically organic dyes are bonded to a probe, which in turn selectively binds to a target molecule. Then the target molecule is identified by exciting the dye molecule, causing it to fluoresce. However, there are many disadvantages to using an organic dye for these fluorescent-labeling systems. The organic dye has a broad emission spectrum (about 100 nm) and broad tails of emission at red wavelengths (about another 100 nm), which results in a severe limitation on the number of different color organic dye molecules which can be simultaneously or sequentially utilized for assays or diagnostics. Organic dyes also often have a narrow absorption spectrum (about 30-50 nm), thus requiring either multiple wavelength probes, or else a broad spectrum excitation source, for sequential excitation of a series of probes respectively excited at different wavelengths. Organic dyes also generally lack photostability, often bleaching or ceasing to fluoresce under repeated excitation.
Semiconducting quantum dots (QDs) have numerous advantages over organic dyes, such as high quantum yield, high molar extinction coefficients (˜10-100× that of organic dyes), broad absorption with narrow, symmetric photoluminescence (PL) spectra (full-width at half-maximum ˜25-40 nm) panning the UV to near-infrared, large effective Stokes shifts, high resistance to photobleaching and exceptional resistance to photo- and chemical degradation. Han et al. (Nat. Biotechnol. 19 631-5) disclosed a porous polymer for multiplexed detection, in which the QDs were embedded in swollen polymer beads. However, embedding does not permit precise control of QD position in the bead; thus the embedded QDs can aggregate and couple with each other inside the beads, which could cause spectral broadening, wavelength shifting, and/or energy transfer. In addition, the poor water-solubility of the polymer bead limits its biological applications.